1. Field of the Invention
The present invention relates to an optical transmission system employing an optical wavelength division demultiplexing system and, more particularly, the present invention relates to an optical demultiplexer device which performs demultiplexing using a reduced number of dispersion compensators.
2. Description of the Related Art
Recently, the number of multiplexed wavelengths in an optical wavelength division multiplexing system has increased, from thirty-two (32) wavelengths, to sixty-four (64) wavelengths, to one-hundred twenty-eight (128) wavelengths. Furthermore, transmission signal speeds have increased from 2.5 Gb/s, to 5 Gb/s, to 100 Gb/s, and capacity has increased.
As transmission signal speeds of wavelength division multiplexing systems increase, the penalty rate increases for the self-phase modulation caused by the group velocity dispersion (GVD) of the optical fiber that is the transmission path. Accordingly, the transmission line necessitates measures to decrease the penalty rate for GVD.
FIG. 12 is a dispersion map showing a relationship between a transmission line and a central wavelength. As shown in FIG. 12, the fiber or optical device having the dispersion value of the transmission path and the opposite dispersion value is inserted into the transmission path, and at a prescribed interval in the transmission path the dispersion value becomes zero. However, because the dispersion characteristics of the transmission path are dependent upon wavelength, when the wavelength division multiplexing system is used, as shown in FIG. 11, even if the dispersion value of the central wavelength is set at zero, the dispersion cannot be set for all the wavelengths.
In order to compensate for the dependence of dispersion value on wavelength, the dispersion is compensated for each wavelength at a reception station. FIG. 10 is a block diagram of a conventional demultiplexer device for performing dispersion compensation at a reception station for a transmission of 4,000 kilometers.
As shown in FIG. 10, the demultiplexer system for dispersion compensation includes optical amplifiers 1-1 through 1-7, dispersion compensators (dispersion compensation fibers) 2-1 through 2-6, a wavelength demultiplexer unit coupler 3, optical filters 4-1 through 4-5, and optical receivers 5-1 through 5-5. Light having respective wavelengths xcex1 through xcex5 is wavelength division multiplexed at an interval of 1 nm. After amplification by the optical amplifier 1-1, the light having a central wavelength of xcex3 is compensated so that it has a dispersion value of zero (0).
After the light from the dispersion compensator 2-6 is amplified by the optical amplifier 1-2, it is separated by the wavelength demultiplexer unit coupler 3 into wavelengths xcex1 through xcex5 and input into optical filters 4-1 through 4-5, respectively, which correspond to each wavelength. The outputs from optical filters 4-1 through 4-5 are amplified by the optical amplifiers 1-3 through 1-7, respectively, and input into dispersion compensators 2-1 through 2-5.
Dispersion compensator 2-1 applies dispersion of +800 ps. Dispersion compensator 2-2 applies dispersion of +400 ps. Dispersion compensator 2-3 applies dispersion of 0 ps. Dispersion compensator 2-4 applies dispersion of xe2x88x92400 ps. Dispersion compensator 2-5 applies dispersion of xe2x88x92800 ps. The outputs of dispersion compensators 2-1 through 2-5 are photoelectrically converted by optical receivers 5-1 through 5-5, respectively.
In the above-described manner, by compensating with different dispersion values using dispersion compensators 2-1 through 2-5, dispersion conversion is performed such that all dispersion volumes between the wavelengths are zero (0).
However, as shown in FIG. 10, when a dispersion compensator corresponding to each wavelength is provided, expensive dispersion compensators require the value equivalent to the compensation value.
It is an object of the present invention to provide a demultiplexer device for demultiplex system which reduces the use of expensive dispersion compensators by half while performing demultiplexing.
It is another object of the present invention to provide a demultiplexing device for demultiplex system which performs demultiplexing without the use of wavelength demultiplexing couplers.
Objects and advantages of the present invention are achieved in accordance with embodiments of the present invention with an optical demultiplexer device for an optical wavelength demultiplexer system, comprising an optical circulator, a dispersion compensator, and an optical filter. A particular wavelength of light is divided by the optical filter, round tripped through the dispersion compensator and output from the optical circulator. A wavelength of light different from the particular wavelength of light passes through the dispersion compensator and optical filter and is output from the optical filter.
Objects and advantages of the present invention are achieved with an optical demultiplexer device, comprising a first optical demultiplexer circuit, including a first optical circulator having a first port, a second port and a third port, wherein multiplexed light is input into the first port, and the light input to the first port is output from the second port, and light input into the second port is output from the third port; a dispersion compensator having an input unit and an output unit, the dispersion compensator being coupled to the second port of the first optical circulator at one of the input or output unit; a first filter coupled to another of the input or output unit to reflect light having a specified wavelength and to transmit light having a wavelength other than the specified wavelength; a second optical circulator having a first port, a second port and a third port, wherein the light transmitted by the first optical filter is input to the first port; and a second optical filter coupled to the second port of the second optical circulator to reflect light having the specified wavelength.
The optical demultiplexer device may further comprise a second optical demultiplexer circuit, including a first optical circulator having a first port, a second port and a third port, wherein multiplexed light is input into the first port, and the light input to the first port is output from the second port, and light input into the second port is output from the third port; a dispersion compensator having an input unit and an output unit, the dispersion compensator being coupled to the second port of the first optical circulator at one of the input or output unit; a first optical filter coupled to another of the input or output unit to reflect light having a specified wavelength and to transmit light having a wavelength other than the specified wavelength; a second optical circulator having a first port, a second port and a third port, wherein the light transmitted by the first optical filter is input to the first port; and a second filter coupled to the second port of the second optical circulator to reflect light having at least one specified wavelength.
In accordance with the present invention, multiplexed light that is branched into a plurality of wavelengths is input into the first port of the first optical circulator of the first optical demultiplexer circuit, and is input into the first port of the first optical circulator of the second optical demultiplexer circuit.
In accordance with embodiments of the present invention, the third port of the first optical circulator of the first demultiplexer circuit is coupled to the first port of the first optical circulator of the second optical demultiplexer circuit.
Objects and advantages of the present invention are achieved in accordance with embodiments of the present invention with demultiplexer device comprising a first unit, including a first optical circulator having a first port, a second port and a third port, wherein multiplexed light is input to the first port, and the light input to the first port is output from the second port, and light input into the second port is output from the third port; a first dispersion compensator having one of an input or an output end connected to a second port of the first optical circulator; and a first filter connected to the other input or output end of the first dispersion compensator to reflect light having a specified wavelength and to transmit light having a wavelength other than the specified wavelength; a second unit, including a second optical circulator having a first port, a second port and a third port, wherein the first port of the second optical circulator is coupled to the third port of the first optical circulator, and light input to the first port of the second optical circulator is output to the second port of the second optical circulator, and light input to the second port of the second optical circulator is output to the third port of the second optical circulator; and a second filter coupled to the second port of the second optical circulator to reflect light having a specified wavelength and to transmit light having a wavelength other than the specified wavelength.
In accordance with embodiments of the invention, the demultiplexer device comprises a plurality of first units and second units, and the first port of the first optical circulator of the first unit is coupled to the third port of the second optical circulator of the second unit, and the first unit and the second unit are respectively consecutively repeated.
Objects and advantages of the present invention are achieved in accordance with embodiments of the present invention with a wavelength division multiplexing device comprising a first wavelength division multiplexing circuit, including an optical coupler to merge light having different wavelengths from a plurality of light sources; an optical circulator including a first port, a second port and a third port, wherein the first port receives an output from the optical coupler, and the light input to the first port is output to the second port, and light input to the second port is output from the third port; a dispersion compensator connected at one of an input or output end to the second port of the optical circulator; an optical filter coupled to an other end of the dispersion compensator to reflect light having a specified wavelength and to transmit light having a wavelength other than the specified wavelength; and an optical coupler to merge the output of the optical filter and the output of the third port of the optical circulator.
The wavelength division multiplexing device may further comprise a second wavelength division multiplexing circuit, including an optical coupler to merge light having different wavelengths from a plurality of light sources; an optical circulator including a first port, a second port and a third port, wherein the first port receives an output from the optical coupler,-and the light input to the first port is output to the second port, and the light input to the second port is output from the third port; a dispersion compensator having an input end and an output end, and coupled at either one of the input or the output end to the second port of the optical circulator; an optical filter coupled to an other end of the dispersion compensator to reflect light having a specified wavelength and to transmit light having a wavelength other than the specified wavelength; and an optical coupler to merge the output of the optical filter and the output of the third port of the optical circulator.
The wavelength division multiplexing device may further comprise an optical coupler to merge outputs of the optical couplers of the first wavelength division multiplexing circuit and the second wavelength division multiplexing circuit.
Objects and advantages of the present invention are achieved in accordance with embodiments of the present invention with an optical wavelength multiplexing device, comprising a plurality of wavelength division multiplexing circuits, each of the plurality of circuits including an optical coupler to merge light having different wavelengths from a plurality of light sources and to output the merged light; an optical circulator having a first port, a second port and a third port, wherein the first port inputs the output from the optical coupler, and the light from the first port is output to the second port, and the light from the second port is output to the third port; a dispersion compensator having an input end and an output end and coupled at one of the input or the output end to the second port of the optical circulator; an optical filter coupled to the other end of the dispersion compensator to reflect light having a specified wavelength and to transmit light having a wavelength other than the specified wavelength; and an optical coupler to merge the respective outputs of the third ports of the optical circulators of the plurality of wavelength division multiplexing circuits.
Objects and advantages of the present invention are achieved with an optical wavelength multiplexing device, comprising a plurality of dispersion compensation units, the respective dispersion compensation units including an optical coupler to merge light having different wavelengths from a plurality of light sources and to output the merged light; an optical circulator having a first port, a second port and a third port, wherein the first port receives the output from the optical coupler, and the light output from the first port is input to the second port, and the light input to the second port is output from the third port; a dispersion compensator having an input end and an output end, and coupled at one of the input or the output end to the second port of the optical circulator; an optical filter coupled to the other end of the dispersion compensator to reflect a specified wavelength and to transmit light having a wavelength other than the specified wavelength; and an optical coupler to merge the output of the optical filter and the output of the third port of the circulator of units of the plurality of dispersion compensation units.